The invention relates to a control process for charge flow management devices mainly as fitted in direct-injection internal combustion engines wherein such charge flow management devices are arranged in intake ports.
In direct-injection internal combustion engines, but also in port-injection type internal combustion engines having intake ports into which no fuel is injected, undesirable fouling of the intake valves will occur due to accumulations of unburnt fuel, combustion gas constituents, and lubricating oil residue. Such fouling is at least in part attributable to the charge flow management devices which, depending on the engine""s operating regime, restrict the fresh-air intake flow or, where multiple intake ports are provided per cyclinder, close off individual ports either partially or fully for the purpose of permitting or optimizing a combustion process in the combustion chamber.
As the engine""s operating regime changes from power output to overrun, the charge flow management devices are placed into their idle position in which they cause the fresh-air supply to be almost fully shut off. For an intake valve arranged in an intake port equipped with a charge flow management device, this constitutes a highly unfavorable operating condition. Upon a load alteration from power output to overrunning, the hot intake valve will be suddenly cut off from its fresh air supply and will cool down but slowly as a result. With the engine on overrun, this throttling effect produces a negative pressure in intake ports equipped with charge flow management devices. This causes more lubricating oil to be drawn into the engine via the valve guides, resulting in increased fouling on the hot valves. Due to the backflow of combustion gases that takes place during the last firing cycle, unburnt fuel, combustion gas constituents and lubricating oil residue will be present in the intake ports. As the charge flow management device closes, this residue is trapped in the intake port for an extended period of time, causing additional fouling.
It is the object of the invention, therefore, to provide a control method for charge flow management devices mainly as fitted in direct-injection internal combustion engines that reduces the amount of intake valve fouling due to unburnt fuels, combustion cast constituents, and lubricating oil residue.